The present invention is based on the discovery that rapid thermal processing (RTP) can convert hydrogen silsesquioxane resin coatings to ceramic silica coatings. This technique is especially valuable for forming protective and dielectric silica layers on electronic devices.
The use of thin film ceramic silica coatings as protective and dielectric layers for electronic devices is known in the art. For instance, U.S. Pat. No. 4,756,977 describes the use of hydrogen silsesquioxane resin derived silica coatings on various substrates including electronic devices. This patent teaches that such substrates may be coated by applying a hydrogen silsesquioxane resin solution to the substrate, evaporating the solvent to deposit a preceramic coating, and then heating to temperatures of 150.degree.-1000.degree. C. in a conventional furnace. The coatings formed thereby provide excellent environmental protection to the underlying substrate and effectively inhibit electrical conduction.
In spite of their efficacy, these conventional methods require the use of a high thermal budget (temperature.times.time) for the oxidation and densification of hydrogen silsesquioxane resin. Such high thermal budgets are not acceptable in many temperature sensitive applications as they may damage or destroy the substrate. This is especially true in the electronic industry where recent advances to reduce device dimensions and increase the number of circuits per wafer put severe constraints on the thermal processing to which a wafer may be subjected.
In an attempt to decrease the thermal budget for hydrogen silsesquioxane resin, researchers have developed various low temperature conversion methods.
Rapid thermal processing (RTP) is a technique for decreasing the thermal budget of a substrate by decreasing the time the substrate is at the elevated temperature. This technique uses high intensity radiation to rapidly heat (50.degree.-300.degree. C./sec) the thin coatings to an elevated temperature for a time which allows the desired physical or chemical processes to be completed but not allow the substrate to be adversely affected. As such, this technique has found applications in the electronics industry including, for example, improving the crystalline quality of semiconductors, annealing ion-implanted single-crystal silicon, annealing ion-implanted polycrystalline silicon, annealing ionimplanted compound semiconductors, annealing metal-semiconductor contacts, forming silicides, forming and annealing dielectrics, and reflowing passivating glasses.
Singh in J. Appl. Phys. 63 (8), 15 Apr. 1988 provides a thorough review of rapid isothermal processing (a synonym for RTP), its mechanism and various applications. Included therein is its use in the formation of thermally grown SiO.sub.2 layers. This reference, however, fails to describe hydrogen silsesquioxane resin as the source of silica.
Similarly, Lassig et al. of Peak Systems, Inc. have described the conversion of various spin-on glass films to SiO.sub.2 coatings by the use of RTP. As with the Singh reference, Lassig et al. fail to describe the use of hydrogen silsesquioxane resin as the source of silica.
The inventors herein have now unexpectedly found that RTP can be used to rapidly convert hydrogen silsesquioxane resin to silica coatings with desirable characteristics such as high density and low film stress